I don't, no. Given that most normal people associate Bitcoin with being cryptocurrency, if it fails to stay on top I suspect that will not set a good image to a lot of people. However, given how low float is for many cryptocurrencies, I do not see it as impossible to overtake Bitcoin on CoinMarketCap, but have my doubts they will overtake in real capital, time, and people invested.

Ethereum has way more security concerns than Bitcoin because it has much more sophisticated scripting for smart contracts - always remember that the more complex you make something, the more possibility of vulnerabilities (a reality we have faced with Ethereum over and over again). You can't fix that - it's a law of nature. It doesn't make Bitcoin superior, it just means Bitcoin is dumber and you literally CAN'T screw it up in the same ways you could Ethereum.

It's too soon to say what will happen in the long-term, but always remember that the most time has been invested in Bitcoin which can't be replaced with money. A lot of altcoins are just Bitcoin's codebase with a few tweaks made. Whether or not sidechains can be securely and practically implemented will be a key question going into the future. As we speak, just seeing Segwit and batching become adopted will clear up the bottlenecks we have in BItcoin now.

This isn't to say there isn't potential in other cryptocurrencies, but rather that it is not as simple as it seems (e.g: Bitcoin is expensive and slow, therefore should be replaced as it is impractical).